According to insurers’ statistics, 80% of oil
tanker accidents which cause oil
spills at sea are a result of human errors: badly handled manoeuvres,
neglected maintenance, insufficient checking of systems, lack of communication
between crew members, fatigue, or an inadequate response to a minor incident
causing it to escalate into a major accident. From a more practical point
of view, analysis of the circumstances surrounding accidents (see animation
“Causes of oil tanker accidents”) demonstrates the high proportion
of spills due to groundings
and collisions.

Wreck of the Aegean Sea by La Coruña, Spain

More information

ITOPF is a mutual organisation providing technical advice on pollution
response for shipowners
of oil tankers. ITOPF experts contribute to response operation management,
impact assessment and environmental restoration operations around the world.
See below the home page of ITOPF’s website, which is an indispensable
source of information on accidents, their causes and response carried out.

Collisions are generally due to manoeuvring errors,
especially in poor visibility and/or busy shipping traffic areas. Groundings
are also often a result of manoeuvring errors, often made worse by high
winds, challenging currents and bad weather.

The grounding of the Sea Empress at the entrance to
Milford Haven port, Wales (Great Britain) is one such example. However,
equipment failure is a more common cause of groundings than of collisions.
The grounding of the oil tanker the Braer in the Shetland Islands, Scotland
(Great Britain), resulting from seawater entering into a fuel tank,
causing engine failure, is a classic example of technical failure.

Oil tanker spills

The International Tanker Owners Pollution Federation Ltd keeps an up-to-date
database on the Internet (www.itopf.com), on oil spills of over 700 tonnes,
from oil tankers, ore carriers and tank barges which have occurred all over
the world since 1967. Information is also provided on various aspects of
the spills and their consequences.

This data brings to light the fact that a little more than 5.5 million tonnes
of oil were spilled in the world’s seas by oil tanker accidents during
the 30 year period from 1970-2000, totalling nearly 182,000 tonnes per year
with a peak of 640,000 tonnes in 1979. Since then, despite a bad year in
1991, the tendency is towards a considerable decrease. In the decade from
1990 to 1999, 73% (830,000 tonnes) of the total amount spilled (1,140,000)
was caused by only 10 accidents.